Hormone-responsive Urinary Incontinence (Urethral Sphincter Mechanism Incompetence)
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Hormone-responsive Urinary Incontinence (urethral Sphincter
Other information that may be useful: How-To Client Education Sheet: How to Collect a Urine Sample
About the Diagnosis
In dogs and cats, as in humans, the flow of urine from the bladder through the urethra is controlled by a complex arrangement of
nerves and muscles. Some of these muscles and nerves form the urethral sphincter, a valve that holds back the urine.
Coordination must exist between the nervous system, bladder, and sphincter to allow a dog or cat to urinate at an appropriate time
and in an appropriate location. Urinary incontinence occurs when an animal is not able to control the flow of urine properly.
There are many causes of urinary incontinence. Among them are neurogenic problems (such as spinal cord trauma) and birth
defects/congenital abnormalities such as ectopic ureters (misplacement of the tubes that leave the kidneys, such that they bypass
the bladder) or other defects of the urinary system or spinal cord. If an animal has a urinary tract infection or urinary stones (calculi),
irritation of the urinary tract will cause a frequent urge to urinate, often in unsuitable places. This gives the appearance of
One of the most common causes of incontinence arises from a problem with the urinary sphincter. It is called urethral sphincter
mechanism incompetence or hormone-responsive incontinence. With this disorder, a weakness of the muscles that control urine
outflow from the bladder allows urine to pass inappropriately. Middle-aged or older, female, spayed dogs are most often affected.
The condition is commonly hormone responsive, meaning that treatment with reproductive hormones is effective in solving the
problem. Young females and older neutered males can also be affected. Medium and large-sized dogs are affected more often than
In this type of incontinence, urine will dribble freely, whenever the bladder is partially full. This happens most often when the dog is
relaxed and when pressure is placed on the bladder (e.g., lying down or sleeping). Often, the most obvious first symptom is a wet
spot on the dogs bed or floor after the dog has rested there. Urine may be observed dribbling from the back end. Sometimes,
prolonged contact with the urine irritates the skin around the vulva, causing redness and a rash (urine scald). Many dogs will lick at
the area, which can make the rash even worse.
Confirming the nature, cause, and best treatment for an animals urinary incontinence is based on a number of factors. These
include the history (features of the problem that you have observed), the veterinarians physical exam findings, and sometimes
simply the response to treatment. It is important to consider other causes of incontinence that could produce indentical symptoms
but require completely different medications or treatments. To determine whether urethral sphincter mechanism incompetence is the
reason for incontinence, your veterinarian may begin by asking you questions that help to better understand key features of your
dogs symptoms, such as:
Is she urinating more frequently than normal, and does it seem uncomfortable?
Is there a recent onset of blood or a foul odor present in the urine?
Does she urinate greater volumes than normal or strain to produce only a few drops?
Is she drinking more or less water than normal?
When does the incontinence occur (i.e., when sleeping versus when awake)?
These questions are important in order to evaluate the likelihood of other causes of inappropriate elimination, such as some of
those mentioned in the second paragraph above. For example, urinary tract infections and bladder stones can result in frequent,
painful urination with or without straining. Kidney disease and diabetes mellitus produce greater volumes of less concentrated urine.
These impostors for urethral sphincter mechanism incompetence must be identified if present, to avoid incorrect or detrimental
Blood tests, a urinalysis (analysis of a urine sample), bacterial culture and sensitivity of the urine (to pinpoint urinary tract
infections), and radiographs (x-rays) or abdominal ultrasound are usually recommended to evaluate whether these other diseases
are present. It is especially wise to have these tests performed on senior animals, since they may have preexisting, age-related
disorders as well.
Living with the Diagnosis
If no other causes of incontinence are found, your veterinarian may arrive at a presumptive diagnosis of urethral sphincter
incompetence, especially if your pet is middle-aged and spayed. Fortunately, this is a hormone responsive disorder in many
female dogs. When we spay young dogs, we remove the uterus and ovaries. These organs are responsible for the production of
many reproductive hormones. In some individuals, the lack of hormones eventually results in weakness of the urethral sphincter. It
is very important to note that the risks of developing a hormone-related problem do not outweigh the benefits of spaying your female
With replacement hormones and other medications, the incontinence can be controlled in virtually all cases, and failure to improve
with medications may indicate a complicating factor (such as urinary tract infection) or a different diagnosis altogether. Usually,
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treatment for urinary sphincter mechanism incompetence is required for life. It may take some time before the problem is solved, and
it can be frustrating during this stabilization period. Additional visits may be necessary to monitor the effect of the medication on
your pet and to make adjustments to therapy. The medication and management is often very effective in improving your dogs
quality of life and making your life with her more enjoyable for years to come. Persistence pays off with successful results in the
majority of cases.
One of two different types of medication is often prescribed:
Replacement hormones (estrogen-based) are used for female dogs. In the rare case of an affected male dog, testosterone
can be given as injections for effective control of the problem. For females, the most common hormonal replacement
medication is called diethylstilbestrol (DES). Recently, media attention has been given to side effects of hormone
replacement therapy (HRT) in humans. Although this treatment is similar to HRT, much smaller doses are used in dogs and
for a shorter period of time. Even though your dog may need to receive this medication for life, the side effects of HRT for
humans do not apply to dogs.
-Adrenergic agonists (phenylpropanolamine [PPA], phenylephrine or pseudoephedrine) can also be prescribed, either
independently or in conjunction with replacement hormones. Some of these medications may not be available at human
pharmacies because of side effects in human medicine.
Both of these types of medications tighten the smooth muscles of the urethral sphincter, which reduces the spillage of urine from the
bladder outward. Treatment is generally affordable but usually must be continued for life.
Often, a medication is given every day for a short period of time. Then the medication is decreased to the lowest possible level that
is still effective. With alpha-adrenergic agonists, this may mean eventually decreasing from every 8 hours (every day) to every 12
hours (still every day), whereas in the case of DES, this often means treating only twice per week with a small amount of the drug. If
a single medication is not completely effective, a combination of medications may offer relief.
Both types of medications have side effects. High doses of diethylstilbestrol can depress the bone marrow. The marrow is
responsible for manufacturing different types of blood cells. Low levels of white blood cells lead to reduced protection from infection.
Low levels of platelets will affect clotting ability. Low levels of red blood cells result in anemia, the most commonly seen side effect,
and in very rare cases this has been fatal. Treatment with DES at high doses will also bring on signs of heat in female dogs (vaginal
swelling and blood tinged discharge). Therefore, low doses are always prescribed, and as a precaution, monitoring that includes
blood tests, is important to detect any of these signs early, since early detection allows reversal of the side effect.
The side effects of -agonists include flushing (red skin, like blushing), panting, elevated heart rate, restlessness, tremors, and
vomiting. These side effects are potentially serious, but not common, and your veterinarian can give you his/her opinion on the
relative risk in a given instance for your individual dog. It is very rare for the risk to outweigh the benefit of treatment.
Another management issue is keeping your dogs hind end clean and dry. The hair may be shaved from the groin area under the tail
(perineum) to make this easier. Your veterinarian can instruct you on how to clean the area, and an antibiotic ointment or cream may
be recommended if a skin infection is present.
Realize that hormone-responsive incontinence is an involuntary disorder. The dog has no sensation of the urination
occurring, and the urine leakage does notindicate a desire on the dogs part to annoy, take revenge, or otherwise